High-entropy alloys (HEAs) are typically defined as alloys containing 5 or more constituent elements each with a concentration between 5 and 35 atomic %. The defining feature of HEAs over other complex alloys is that, due to their high entropy of mixing, they essentially consist of a simple solid solution phase, rather than forming one or more intermetallic phases. Various HEAs exhibit one or more superior mechanical properties such as yield strength, fracture toughness, and fatigue resistance. Multi-principal element alloys (MPEAs) are similar to HEAs but may include as few as four constituent elements. However, many HEAs and MPEAs, particularly those that include one or more refractory metals (e.g., Nb, Mo, etc.) are quite difficult to fabricate and utilize due to their high strength and limited ductility. Because diffusion tends to be quite slow in HEAs and MPEAs, bulk quantities of these materials are also often quite difficult to homogenize. These and similar issues have limited the widespread adoption of many HEAs and MPEAs.
Additive manufacturing, or three-dimensional (3D) printing, is a widely utilized technique for rapid manufacturing and rapid prototyping. In general, additive manufacturing entails the layer-by-layer deposition of material by computer control to form a three-dimensional object. Most additive manufacturing techniques to date have utilized polymeric or plastic materials as raw materials, as such materials are easily handled and melt at low temperatures. Since additive manufacturing involves the melting of only small amounts of material at a time, the process has the potential to be a useful technique for the fabrication of large, complex structures composed of HEAs or MPEAs. Specifically, the small melt pool of material utilized at any point in time during an additive manufacturing process may result in small molten volumes of substantially homogenous alloy material that cool at a rate sufficient to stabilize the homogenized composition of the alloy. That is, the small size of the melt pool should promote mixing of the alloy constituents, and the high cooling rate should limit segregation, promoting formation of a substantially homogeneous alloy.
Unfortunately, additive manufacturing of metallic materials is not without its challenges. When metallic precursor materials for additive manufacturing possess significant amounts of oxygen or other volatile species (e.g., calcium, sodium, antimony, phosphorus, sulfur, etc.), the melting of such materials may result in sparking, blistering, and splattering (i.e., ejection of small pieces of the materials themselves). In addition, even if a three-dimensional part is fabricated utilizing such materials, the part may exhibit excessive porosity, cracking, material splatter, and insufficient density and machinability.
In view of the foregoing, there is a need for improved precursor materials for the additive manufacturing of metallic parts, and in particular parts composed of HEAs and MPEAs.